The invention relates to papermaking machinery and methods. The invention relates more particularly to improvements in the dry end of a tissue machine enabling a close coupling between a dryer and a reel-up where the finished paper web is wound into a roll and enabling improved control of nip load in the reel-up.
In the production of high-quality tissue, machine speed and efficiency are often limited by the performance of the dry end of the machine between the final dryer and the winding station or reel-up. Tissue is extremely delicate and difficult to handle, especially at high machine speeds. As the machine speed is continually pushed higher and higher in an effort to improve productivity, it becomes increasingly difficult to move the tissue web from the dryer to the reel-up without encountering handling problems. In a typical tissue machine, the web is creped from a Yankee dryer by a creping doctor and is then carried in a partly open or free draw to the reel-up. Located in this free draw is a measuring frame supporting measuring equipment for measuring properties of the web such as basis weight and moisture content. The dry end of the machine frequently also includes calendering equipment. In many tissue machines, the free draw tends to be quite long, which exacerbates the problem of handling the web. The web typically is guided to a reel drum that forms a nip with a growing paper roll wound on a reel spool of the reel-up. In most cases, the reel drum is mounted in a fixed position and the reel spool is movable for controlling the nip load in the reel-up.
The conventional type of tissue machine described above has a number of drawbacks that limit the machine speed and/or the quality of the tissue and the uniformity of the properties of the wound roll. The long distance between the creping doctor and the reel-up is conducive to aerodynamic instabilities of the web, which can cause web breaks and other problems. The web stability problems typically necessitate supporting equipment to stabilize the web. The supporting equipment commonly consists of a relatively sophisticated series of foils and/or guide rolls. The long dry end also means that the machine has a relatively large footprint.
Another problem associated with the conventional tissue machine is that because of the great weight of the paper roll it is very difficult to accurately control the nip load by moving the reel spool on which the paper roll is wound. Consequently, nonuniformities in the winding qualities of the paper roll can arise.
The above needs are met and other advantages are achieved by the present invention, which provides apparatus and methods for a dry end of a tissue machine enabling the length from the dryer to the reel-up to be shortened substantially, thus alleviating many of the problems associated with long dry ends as noted above. According to one aspect of the invention, an apparatus for a dry end of a tissue machine includes a rotatable reel spool onto which the paper web is wound to form a paper roll, and a stabilizing foil assembly extending from the dryer to the paper roll. The foil assembly in some embodiments has a downstream edge that forms a nip with the paper roll through which the paper web is guided onto the paper roll. In other embodiments, the foil does not form a nip with the paper roll, in which case there can be a very short free draw between the downstream edge of the foil and the paper roll. Where the foil assembly forms a nip with the paper roll, the foil assembly can be movable relative to the reel spool for controlling the nip load in the nip. Advantageously, the foil assembly can be rotatable about a pivot axis for controlling the nip load. Alternatively or additionally, the foil assembly can include a downstream edge portion that is flexible and bears against the paper roll to form the nip. The flexible edge portion can be backed up by a movable support member whose positioning is controlled for controlling the nip load, or the foil assembly or the downstream portion thereof can be pivotally movable for controlling the nip load. In some embodiments, the foil assembly comprises a single foil that extends from the dryer to a position proximate the paper roll in the winding position; in other embodiments, the foil assembly comprises two (or more) foils that collectively extend from the dryer to the paper roll.
Preferably, one or more measuring sensors are disposed proximate the foil for measuring properties of the paper web such as basis weight and moisture. The sensor or sensors can be supported by the foil or on a structure mounted adjacent the foil. The sensors can include a traversing sensor that is movable in the cross-machine direction for measuring web properties at various locations along the cross-machine direction. The sensor can be mounted adjacent an opposite side of the foil from the web, in which case the foil can include a slot aligned with the sensor so that the sensor can view the web. The foil can include a movable cover for covering the slot when the sensor is not measuring web properties. The foil can be an ordinary foil, or alternatively can be an active foil that creates a directed air flow for supporting and assisting the paper web""s movement.
In some embodiments of the invention, the dryer of the paper machine includes a Yankee dryer as the final drying device, and the web is scraped from the Yankee dryer by a creping doctor. The reel spool is rotatably driven and can be positioned, in some embodiments, in an upper position with respect to the foil. In the upper position, the reel spool rotates in the opposite direction to that of the dryer roll from which the web is creped, and the downstream edge of the foil guides the web onto the lower side of the paper roll. In other embodiments, the reel spool is in a lower position relative to the foil, in which case the reel spool rotates in the same direction as the dryer roll and the foil guides the web onto the upper side of the paper roll.
In another aspect of the invention, an apparatus for the dry end of the machine includes a rotatable reel drum mounted adjacent the reel spool so as to form a nip with a growing paper roll wound on the reel spool, the paper web being supported and guided onto the paper roll by the reel drum. A calendering belt forms a calendering nip with the reel drum for calendering the paper web, the paper web passing through the calendering nip prior to being wound onto the paper roll. The load in the calendering nip can be controlled by varying the belt tension.
In accordance with still another embodiment of the invention, the dry end includes a rotatably driven reel spool for winding the paper web thereon located downstream of the dryer, a belt stretched between at least a pair of spaced-apart guide rolls and forming a nip with a growing paper roll wound on the reel spool, and a stabilizing foil for supporting and stabilizing the paper web exiting from the dryer. The foil has an upstream end adjacent the dryer and a downstream end proximate the nip such that the paper web is supported by the foil from the dryer to the nip.
In a still further embodiment of the invention, the foil can be eliminated and its stabilizing function can instead be performed by the belt. The belt is looped about a plurality of guide rolls, a first of the guide rolls being positioned proximate the dryer and spaced upstream of a growing paper roll wound on the reel spool, and a second of the guide rolls being positioned adjacent the paper roll. A portion of the loop of the belt between the first and second guide rolls extends from a location proximate the dryer to the paper roll. This portion of the loop stabilizes the paper web and guides the paper web onto the paper roll at a nip formed between the belt and the paper roll.
The invention can also be practiced in tissue machines having one or more through-air dryers (TADs) as the final drying devices. In one embodiment, the paper web is carried, supported on a TAD fabric forming an endless loop, through one or more TAD units. The TAD fabric carrying the web thereon exits the last TAD unit and is guided by guide rolls such that the TAD fabric forms a nip with a building paper roll in the reel-up, thus guiding the web onto the building paper roll. Accordingly, the paper web is continuously supported by the TAD fabric from the dryer to the reel-up.
The invention also encompasses improvements in controlling the nip load in the reel-up. In some embodiments, a reel-up includes a rotatable reel spool mounted in a fixed location, and a movable reel drum forming a nip with the paper roll on the reel spool. Nip load is controlled by moving the reel drum. The weight of the reel drum is constant during winding, unlike that of the paper roll. Consequently, it is much easier to control the nip load accurately by moving the reel drum than by moving the variable-weight paper roll. Moreover, the reel drum can be made much lighter in weight than the paper roll, which further facilitates accurate nip load control since it is easier to move a light-weight drum accurately than it is to do so with a heavy paper roll.
In other embodiments, the reel-up includes a holder that holds the reel spool and is pivotable about a pivot arrangement that is movable for controlling the nip load in the reel-up. The nip load in an advantageous method embodiment of the invention is controlled by moving the pivot arrangement with a component of movement that is parallel to a plane in which the axes of the reel spool and the reel drum lie. When the paper roll on the reel spool is fully wound, the holder can be rotated about the pivot arrangement to deliver the paper roll to a further processing station, for example by releasing the reel spool and paper roll onto rails or other suitable supports along which the paper roll can be moved.
The invention in other embodiments also provides a composite shaftless core that can be used in place of the steel core shaft and paper core conventionally used for winding paper. The composite shaftless core can be constructed of a fiber-matrix composite material and advantageously includes metal bushings or fittings at the ends for connection with chucks and/or drive units. The metal fittings may include teeth or splines for engagement by drive units. The composite shaftless core can be used directly in further operations such as converting, thus eliminating the need for rewinding before converting. In a preferred embodiment of the invention, the tubular side wall of the composite shaftless core is perforated with holes and the shaft can be connected to a vacuum source in order to create an underpressure inside the shaft to cause a paper web to be suctioned against the shaft at the start of a winding operation.